Make sure that empty string is filtered out when we get the secondary jars from conf

Author: DB Tsai <dbtsai@dbtsai.com>

Closes #1027 from dbtsai/dbtsai-classloader and squashes the following commits:

9ac6be3 [DB Tsai] Fixed line too long
c9c7ad7 [DB Tsai] Make sure that empty string is filtered out when we get the secondary jars from conf.